Countershaft transmissions are widely used in the drives lines of vehicles such as wheel loaders, earthmoving tractors, and other off-highway vehicles because the plurality of rotating clutch assemblies and associated gears can be so positioned on the usual parallel shafts as to allow considerable flexibility in adapting them to different space requirements and to different drop heights between the input and output axes. Moreover, a substantial number of simple parts and/or similarly sized parts can be used for manufacturing economy. Exemplifying the art in this area are the following U.S. Pat. Nos.: 3,080,767 issued Mar. 12, 1963 to S. J. Price, Jr.; 3,425,293 issued Feb. 4, 1969 to H. S. Krawczyk, et al; 3,465,609 issued Sept. 9, 1969 to J. F. Fisher, et al; 3,858,455 issued Jan. 7, 1975 to R. L. Sisson, et al; 3,913,616 issued Oct. 21, 1975 to J. Horsch; and 4,341,127 issued July 27, 1982 to E. Stodt.
While such countershaft transmissions have a considerable number of advantages, they are deficient in several other respects. One problem is that if the input member of several of these transmissions is connected to the engine and/or optional hydrodynamic torque converter excessive space is required above the axis of the input shaft. Specifically, it would be necessary in several vehicular applications to raise the floor plates and elevate the entire operator station in order to obtain sufficient clearance above the input shaft's axis to accommodate large diameter components such as a rotating clutch thereat.
Another factor of significance is that some of these transmissions have an excessive axial length so they cannot fit into the limited space available in a vehicle. In this regard planetary transmissions employing a considerable number of interconnected planetary gear sets are also known which can provide a plurality of forward and reverse speeds as can be noted by reference to the following U.S. Pat. Nos.: 3,347,113 issued Oct. 17, 1967 to C. A. Ramsel and 3,954,028 issued May 4, 1976 to W. E. Windish. But these transmissions are arranged along a single axis and are of an undesirable length. Also the known planetary systems are not compatible with the increased number of speeds and step ratios required for a tillage-type agricultural vehicle, and require an extra transfer gear train to drop the drive from the upper input axis to the lower output axis aligned with the ground engaging drive members of the vehicle.
Furthermore, a transmission is needed which can provide at least six forward speeds, and preferably ten forward speeds, and at least two reverse speeds and can effectively match such vehicular speed requirements with a relatively small elevational drop requirement between the input and output axes. In addition, the transmission should be able to provide a power take-off option operable at the speed of the input shaft and various hydraulic pump drive options in relatively nested locations so as to not unduly extend the overall dimensions of the transmission.
One drive train for a motor grader which has received wide commercial acceptance is disclosed in U.S. Pat. No. 3,815,445 issued June 11, 1974 to J. M. Gorrell, et al and in U.S. Pat. No. 3,894,603 issued July 15, 1975 to J. E. Winzeler, both of which are assigned to the assignee of the present invention. In general, that motor grader power train has a leading range section of the countershaft drop box type employing one forward clutch assembly and one reverse clutch assembly and a trailing speed section of the multiple planetary gear set type that can provide a plurality of speeds for each range of the leading section. In actual use eight forward speeds and eight reverse speeds are available to the vehicle operator. However, the speed steps thereof are not favorably grouped for use in an agricultural tillage-type vehicle operation, and the transmission is relatively complex while being limited to but eight forward speeds.
Other multispeed transmissions have been considered which employ serially arranged range and speed sections as can be appreciated by reference to the following U.S. Pat. Nos.: 3,149,498 issued Sept. 22, 1964 to M. J. Mack; 3,377,885 issued Apr. 16, 1968 to R. M. Tuck, et al; and 4,063,464 issued Dec. 20, 1977 to E. R. Crabb. Still another transmission is disclosed in SAE Paper No. 750818, entitled "The TDMC-33-7002: A 1500 HP Transmission for Shuttle Type Vehicles" presented by J. B. Snoy, et al on or about Sept. 8-11, 1975. These transmissions are also not conveniently adaptable to all of the needs mentioned above.
Accordingly, what is needed is a simple, rugged and compact leading countershaft transmission that can provide at least two forward ranges and one reverse range, and which is preferably compatible with a wide variety of trailing transmissions that can provide a plurality of speeds for each range of the countershaft transmission. In addition, the countershaft transmission should be containable in a simple housing, be capable of convenient servicing, be radially compact along the input axis, and be adaptable to a moderate drop height between the input and output axes. And, still further, the transmission should be able to provide both a power take off (PTO) option and positive drive to a plurality of hydraulic pumps or other auxiliary devices at a speed which is a function of the input speed and which is not affected by any gear change of the transmission.